300 Observations on the 



interruption, it be supposed that the light is reflected from a 

 more elevated portion of the ridge. The former supposition 

 better explains those instances, in which, like the present, the 

 illumined spot lies in the lower limb ; the latter is more appli- 

 cable to such, as, like that mentioned by M'Laurin, have it 

 in the upper margin. It is obvious also, that when the direction 

 of the reflected rays was so depressed as not to appear above 

 the summits of the ridge, a solitary speck of light, such as 

 seen by Short, would alone be observed. 



In the preceding investigation of one class of phenomena 

 from which the agency of a lunar atmosphere is inferred, no 

 other principles of discussion, except those derived from actual 

 observation, have been admitted; the inequalities of the moon's 

 surface, and reflection of the solar rays. That the effects de- 

 scribed, are at least intimately connected with these causes, still 

 further appears from the fact, that in those eclipses in which the 

 former have not been clearly perceived, these luminous streams, 

 flashes,and spots have not been observed. Thus, Weidler states, 

 that on one occasion, although very distinctly marked, the out- 

 line of the moon's disc appeared without any elevations or 

 depressions, such as he had formerly seen, and even attempted 

 to measure ; as also unaccompanied by any of those in- 

 dications of an atmosphere which he had previously noticed. 

 " Ceeterum lunse discus, sub sole, peripheriam accurate termi- 

 natam, absque ulla inequalitate nee non faciem nigerrimam 

 ostendit. Nullum quoque atmospherice orbi lunas insidentis 

 vestigium potuit deprehendi*". On the whole, therefore, it 

 may be concluded, that from the appearances now described, 

 no proofs of a lunar atmosphere can be deduced. 



* Phil. Trans- vol. xli. p. 94, Weidler appears to have paid great attention 

 to the observation of solar eclipses, with a view to establish the hypo» 

 thesis of a lunar atmosphere. He has published details of several, of con- 

 siderable luaguitude, in which he ascribes various streams of light, Sfc. to 

 atmospheric effects, and adds, that fie not only saw them, but "guadeiis 

 vidit." On all these occasions the mountains were very conspicuous, the 

 depth of one valley is estimated at ^ of a diameter. 



